Instructions

1. Make the pastry: Position a rack in the center of the oven and preheat to 425°F. Line a baking sheet with parchment. To a medium heavy pot over high heat, add the butter, milk, salt, sugar, and ¼ cup of water and bring to a boil. Remove from the heat and beat in the flour with a wooden spoon. Return the pot to medium heat and cook, beating vigorously with the spoon, until the mixture forms a thick dough and pulls away from the sides of the pot, about 2 minutes. Transfer the dough to a medium bowl. Mix in one-third of the eggs at a time, beating constantly with the spoon after each addition, until the dough is smooth.
2. Transfer the dough to a pastry bag fitted with a plain round ½-inch tip. Pipe 12 to 13 mounds of dough, each about 1½ inches wide, on the prepared baking sheet, spacing about 1 inch apart, then dust the mounds with the confectioners sugar. Transfer to the oven, immediately turn the temperature to 400°F, and bake until puffed and deep golden brown, 15–18 minutes. When cool enough to handle, transfer the puffs to a wire rack to cool completely.
3. Make the chocolate sauce: In a medium pot over medium-low heat, bring 2 inches of water to a simmer. To a medium heatproof bowl, add the chocolate. Place the bowl over the pot and cook, stirring frequently, until the mixture is smooth and the chocolate has melted, about 5 minutes. 
4. Meanwhile, in a second medium pot over medium heat, bring the milk to a simmer. Add the cream and return to a simmer. Add the melted chocolate, sugar, and butter and whisk until smooth. Keep the sauce warm. 
5. To assemble the profiteroles, make a wide incision in the side of each puff. Fill each puff with a small scoop of ice cream. Spoon the warm chocolate sauce over the puffs and serve immediately.